Thesis
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(2023)ThesisEngineered Cementitious Composite (ECC) is a high-performance cementitious material with notable mechanical properties. It is recommended for bridges, high-rise buildings, and industrial facilities that experience a wide range of loads. While ECC exhibits significant bendability and energy absorption capability, it is vulnerable to impact loads. Biomimetic design, inspired by nacre, offers a solution to enhance the structure’s resilience. This thesis investigates the behaviour of nacre inspired designs in improving the structural behaviour and resilience of metre-scale ECC structures under various mechanical loading conditions. A high-strength ECC was developed with polyethylene (PE) and steel fibre and its mechanical properties were comprehensively studied in compression, tension, and bending. Test results indicated that the PE fibre lengths had a significant effect on the quasi-static force-displacement curves. However, under low-velocity impact (3.5 m/s to 4.5 m/s) no such effect was observed. Further, monolithic ECC beams were brittle. Nacre's features were introduced into the design of ECC beams to improve the mechanical response. Four designs were cast and tested under three-point bending, including a monolithic beam and three bioinspired designs mimicking nacre's body structure. Results demonstrated that the nacre inspired designs exhibited significantly higher ductility, energy absorption, and resistance to impact loads compared to monolithic beams. Nacre's features were also integrated into panel structures. Quasi-static punch tests on these panels showed that bioinspired designs exhibited superior structural performance including increased ductility, energy absorption capacity and flexural compliance compared to monolithic panels. High-velocity impact tests (620 m/s to 640 m/s) on ECC panels using a 16 mm spherical steel projectile revealed that monolithic panels experienced a catastrophic failure. In contrast, bioinspired panels demonstrated local bulging, resulting in significantly less damage on their front and back surfaces, despite having a similar penetration resistance. Finite element models were developed using Abaqus to simulate the behaviour of ECC panels. The models incorporated material and geometric nonlinearity, layered configurations with hyperelastic adhesives, fibre mesh, and cohesive interactions. The models were validated through comparison to experimental results, including force-displacement curves and failure modes. The models agreed well with the experimental results. This thesis has developed a high-strength ECC material by incorporating a hybrid combination of PE, steel fibres, and fly ash. The incorporation of fly ash offers sustainability and holds promise for utilization in various infrastructure undertakings. Furthermore, nacre-inspired designs have demonstrated improved mechanical properties, including heightened ductility and enhanced energy absorption. Moreover, when subjected to high-velocity impacts, these nacre-inspired structures exhibited minimal damage, signifying their ease of maintenance and reduced risk of debris-related hazards.
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(2023)ThesisThis thesis focuses on the environmental impact of car-following (CF) driving behavior in mixed autonomy traffic. Given the shortage of real-world mixed autonomy trajectory data, this area of research is not yet well-understood and is often explored using classical simulation models with assumed and unvalidated parameters with little or no consideration of autonomous eco-driving behavior. The thesis introduces a new calibration framework applicable to various CF models. The framework uses the concept of ‘adaptability’ which improves the simulation of AVs’ driving behavior by enabling real-time changes of the CF model parameters based on prevailing traffic conditions. The thesis also provides an environmental assessment of mixed autonomy traffic considering different vehicle arrangements in a platoon using real data and simulation outcomes. The thesis provides several novel findings regarding the impact of the driving behavior of AVs on-road emissions. For instance, the analysis of the trade-off between traffic stability and mobility in a mixed autonomy environment reveals that an automated eco-driving strategy that minimizes the reciprocal of the platoon average velocity produces fewer emissions compared to strategies that aim to minimize traffic instability measured by the standard deviation of velocity or average acceleration. This is because the latter can considerably decrease the platoon average velocity to increase stability. In addition, vehicle arrangements, specifically whether the AV is leading or following, affect the AV’s driving behavior and thus, the emissions, especially in congested conditions. Furthermore, the correlation between mobility and emissions shows that traffic emissions are highly influenced by acceleration at a high-velocity level and by time headway at a low-velocity level. Overall, the thesis explores the environmental implications of AV driving behavior considering different aspects such as traffic network, market penetration rate, and vehicle arrangements. Therefore, the findings of this thesis can be insightful at this early stage of AV deployment to ensure that the future mixed autonomy environment does not only improve traffic and safety but also contribute to a more environmentally friendly transport system.
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(2023)ThesisThe goal of this thesis is to provide information that will help to restore sites degraded by human activities such as mining and poor agricultural practices. Agricultural production is the backbone of societal development, yet some practices employed by farmers can reduce the ability of the farms to produce the food and fibre society needs. Practices such as replacing perennial vegetation with ephemerals, over-fertilization, improper irrigation, and overgrazing are the major causes of agricultural land degradation. These practices severely alter the topsoil which contains beneficial microorganisms that promote plant establishment. However, restoration projects on degraded lands rarely consider microorganisms. Literature synthesis revealed that inoculating microorganisms to plants increases plant growth by 47%. Thus, the lack of microorganisms in land restoration may explain why efforts to recruit plants from seed during restoration projects have yielded mixed success. The lack of consideration of microbes in restoration projects led me to develop the first microbial-inoculated soil seed moulds for restoration. The soil seed mould is a seed enhancement technique that embeds seeds in microbial-inoculated soils moulded in concave trays. The microbial-inoculated soil seed mould was tested on two native species: Triodia epactia and Acacia inaequilatera, in a mine-degraded field. Soil seed moulds inoculated with microorganisms increased seedling emergence but had no effect on seedling survival, and sometimes had a negative effect on plant growth. The microbial-inoculated soil seed mould also changed the microbial community composition in the soil without affecting microbial diversity. The results show that benefits obtained from microorganisms are only achieved at the early stages of plant establishment. My study revealed that the effect of microorganisms on ecosystem services during dryland restoration can vary from limited positive effects on some specific ecosystem components to no effect (likely due to the high mortality of inoculated microorganisms), to detrimental effects on plant growth. These mixed microbial effects reflect the dynamic behaviour of microorganisms in soils, suggesting the need to build a stronger understanding of the mechanisms that influence microbial behaviour in soils. I hope that my thesis inspires microbial ecologists to develop more effective microbial strains that persist in soils and provide continuous benefits to the ecosystem.
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(2023)ThesisMemory corruption vulnerabilities can lead to memory attacks. Three of the top ten most dangerous weaknesses in computer security are memory-related. Memory attack is one of a computer system’s oldest but everlasting problems. Companies and the government lost billions of dollars due to memory security breaches. Memory safety is paramount to securing memory systems. Pointer-based memory safety protection has been shown as a promising solution covering both out-of-bounds and use-after-free errors. However, pointer-based memory safety relies on additional information (metadata) to check validity when a pointer is dereferenced. Such operations on the metadata introduce significant performance overhead to the system. Existing hardware/software implementations are primarily limited to proprietary closed-source microprocessors, simulation-only studies, or require changes to the input source code. In order to provide the need for memory security, we created a memory-safe RISC-V platform with low-performance overhead. In this thesis, a novel hardware/software co-design methodology consisting of a RISC-V based processor is extended with new instructions and microarchitecture enhancements, enabling complete memory safety in the C programming language and faster memory safety checks. Furthermore, a compiler is instrumented to provide security operations considering the changes to the processor. Moreover, a design exploration framework is proposed to provide an in-depth search for optimal hardware/software configuration for application-specific workloads regarding performance overhead, security coverage, area cost, and critical path latency. The entire system is realized by enhancing a RISC-V Rocket-chip system-on-chip (SoC). The resultant processor SoC is implemented on an FPGA and evaluated with applications from SPEC 2006 (for generic applications), MiBench (for embedded applications), and Olden benchmark suites for performance. The system, including the RISC-V CHISEL, compiler, profiling and analysis tool-chain, is fully available and open-source to the public.
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(2023)ThesisShifting patterns in consumption and the inadequate disposal of wastes has led to the escape of anthropogenic debris into the marine environment. The growing volume of debris, both within and entering coastal and marine areas, has prompted global concern over the risks they may pose to environmental and human health. Responses to curb further entry and address debris already within the environment include several management interventions, informed by policies and legislation. Effective debris management requires an understanding of potential sources, subsequent dispersion and an estimate of the risks posed to habitats and biological assemblages, which could be attained through environmental monitoring. Monitoring across relevant spatio-temporal scales, however, is often outside the reach of formal government and research programs and there is a growing recognition of the role citizen science data may play in debris management and decision making. This thesis aims to bridge environmental monitoring with policy and decision making, combining citizen science with other data into an evidence-base for management. The thesis assesses several citizen science datasets from a local to Federal scale to identify debris trends and their drivers (Local: four estuaries; State: Queensland; Federal: Australia). Further, I combine expert elicitation and empirical debris data to assess the risk posed by debris. I provide a framework for linking debris identified within the environment to economic sectors, as part of a formal accounting framework. The thesis also provides methodological guidance to refine citizen science sampling during monitoring programs, to improve the accuracy and reliability of resulting datasets. Through careful application and consideration of data quality, citizen science data could be used to supplement formal monitoring efforts to better understand and address the challenge of marine debris. This thesis advances the role of citizen science beyond environmental monitoring to inform management efforts at scale.